Optical element, illumination device, and projection display device

Abstract

An optical element that is capable of reventing an increase in size while increasing the light intensity of fluorescent light includes: a light-guide plate ( 21 ) that propagates light incident from a light source ( 1 ); a phosphor layer ( 22 ) that is provided on the light-guide plate ( 21 ) and that generates fluorescent light by means of light from the light-guide plate ( 21 ); a metal layer ( 23 ) that is layered on the phosphor layer ( 22 ); and a diffraction grating that is formed at the interface of the phosphor layer ( 22 ) and the metal layer ( 23 ).

1 . An optical element comprising:
 a light-guide plate that propagates light that is incident from a light source;   a phosphor layer that is provided on said light-guide plate and that generates fluorescent light by means of the light from said light-guide plate; and   a metal layer that is layered on said phosphor layer;   wherein a diffraction grating is formed on the interface of said light-guide plate and said phosphor layer.   
     
     
         2 . The optical element as set forth in  claim 1 , further comprising a wavelength-selective part that is provided on the surface of said light-guide plate that is opposite the surface on which said phosphor layer is provided, that reflects light that is incident from said light source, and that transmits and emits fluorescent light generated from said phosphor layer. 
     
     
         3 . The optical element as set forth in  claim 2 , further comprising a structure that is provided on said wavelength-selective part and that suppresses reflection of said fluorescent light. 
     
     
         4 . The optical element as set forth in claim  13 , wherein said diffraction grating is an uneven structure formed on said light-guide plate. 
     
     
         5 . The optical element as set forth in  claim 1 , wherein said phosphor layer includes metal fine-particles in which surface plasmons are excited by light from said light-guide plate. 
     
     
         6 . The optical element as set forth in  claim 1 , wherein the effective dielectric constant on the light guide body-side of said metal layer is at the upper limit of a range wherein the real part of the effective dielectric constant of the medium that is closer to said light-guide body-side than said metal layer does not surpass the absolute value of the real part of the dielectric constant of said metal layer. 
     
     
         7 . The optical element as set forth in  claim 6 , wherein said effective dielectric constant is determined based on:
 the dielectric constant distribution of the dielectric of the medium that is closer to said light-guide body-side than said metal layer; and   the distribution of surface plasmons with respect to the direction perpendicular to the interface of said metal layer in the medium that is closer to said light-guide body-side than said metal layer.   
     
     
         8 . An illumination device comprising:
 the optical element as set forth in  claim 1 ; and   a light source that irradiates light to the light-guide plate of said optical element.   
     
     
         9 . A projection image display device comprising the illumination device as set forth in  claim 8 .